Think technology and it's not hard to see dollar signs. But California and the West have many free and geeky places worth visiting; you just have to know where to look. My new book, "The Geek Atlas" (O'Reilly Media, 542 pages, $29.99), details 128 places around the world where geeks go wild. Here are five in California and Nevada that won't cost a dime to visit.

1. Computer History Museum

Visitors to Boston in the late 1980s might have dropped in on the Computer Museum; it used to have the best collection of computer equipment anywhere in the world. But since 2002, its collection plus many additional pieces have been on display in the old Silicon Graphics headquarters in Mountain View. There's simply no better place to go to understand the history of computing and see an 1889 Hollerith Census Machine that used punched cards, a preserved copy of Microsoft Windows 1.0, the Honeywell Kitchen Computer with its sexist advertising ("If she can only cook as well as Honeywell can compute") and a collection of micro, mini and supercomputers. 1401 N. Shoreline Blvd., Mountain View. www.computerhistory.org, (650) 810-1010.

In 2003, the Human Genome Project announced the sequencing of the complete human genome. The sequence of 3 billion A's, T's, C's and G's (that represent the four chemicals found in DNA) had been deciphered. A lot of that work had been done in Walnut Creek at the Joint Genome Institute, where long strands of DNA were split into tiny shreds, inserted into E. coli bacteria, multiplied over and over, extracted, made to fluoresce in four colors, and then read by robots. The work continues today sequencing the genomes of bacteria, animals, fish, plants and viruses. And the Joint Genome Institute offers a free tour, by reservation only at www.jgi.doe.gov or (925) 296-5643. 2800 Mitchell Dr., Walnut Creek.

3. Goldstone Deep Space Communications Complex

More than 30 years ago, NASA launched the Voyager 1 probe, which continues to phone home from the edge of the solar system. Our own ET's call gets answered at Fort Irwin. The rugged landscape here, which was used to train Apollo astronauts, is dotted with massive dishes that hunt for faint signals from distant space probes in order to receive pictures and information about our solar system. Goldstone offers free tours during the week that must be booked in advance. There's a museum detailing the science and history of deep-space communication and a guided tour (for which you'll need your car) of the site and its dishes. Fort Irwin. deepspace.jpl.nasa.gov, (760) 255-8688.

4. The Company Store

You're not a true Apple fan until you've visited the Company Store. It's not an Apple Store, you can't buy computers, iPhones or iPods, but it is the only store inside Apple's Cupertino headquarters. The Company Store was originally reserved for Apple employees but has been opened to the public and sells what can only be described as Apple swag: hats, T-shirts, mouse pads and more all emblazoned with the Apple logo. With all the money you've saved from the other four places, you can treat yourself to the Apple fanatic's ultimate badge of honor: an "I visited the Mothership" black T-shirt. Open only on weekdays. 1 Infinite Loop, Cupertino, www.apple.com/companystore, (408) 974-5050.

Between 1951 and 1992, the U.S. set off more than 1,000 nuclear explosions outside Las Vegas in an area known as the Nevada Test Site. Once a month it's possible to take a tour of its 1,350 square miles of dry lake beds and see the bomb craters and ground zeros. Visitors see everything from the remains of the buildings familiar to anyone who's seen old civil defense films of houses exploding in flames after a nuclear blast, to the enormous Sedan crater made as part of Operation Plowshare (an attempt to use nuclear weapons for civilian purposes like mining), to an old bank vault that survived a nuclear blast. With one tour a month, reservations are required months in advance. 755 E. Flamingo Road, Las Vegas. www.nv.doe.gov/nts/tours.htm. (702) 295-0944. Visitors need to bring their own food and drink, and wear rugged clothing (especially shoes).